As one form in shutdown methods for a reforming apparatus, there has been know one which is described in Patent Document 1. As shown in FIG. 4 of Patent Document 1, in a shutdown method for a polymer electrolyte fuel cell, combustible gas is purged by flowing steam within a reformer system at the time of shutdown, after which steam within the reformer system is purged by introducing air into the reformer at a time point when the temperature of reforming catalyzer in the reformer goes lower than the temperature at which the reforming catalyzer oxidizes. Further, as shown in FIG. 5 of Patent Document 1, in a shutdown method for a polymer electrolyte fuel cell, combustion exhaust gas from the reformer is introduced into a CO oxidizing unit instead of introducing air and is in turn flown through a CO metamorphose unit and the reformer to purge the reformer system.
As another form, there has been known one which is shown in Patent Document 2. As shown in FIG. 4 of Patent Document 2, in a shutdown method for a reformer for a polymer electrolyte fuel cell, in lowering the temperature of a reforming catalyzer layer in a reformer reforming section at the time of shutdown, reformed gas in the reformer is purged by steam, after which the temperature of the reforming catalyzer layer is lowered to a temperature or lower at which material gas is not pyrolyzed and which is equal to or higher than a condensation temperature for steam, and then, the material gas is introduce to purge the steam within the reformer. Further, the exhausted material gas is temporally burned at the reformer reforming section.
As another form, there has been known one which is shown in Patent Document 3. As shown in FIG. 9 of Patent Document 3, in a shutdown method for a reformer, cooling is performed by flowing a mixture gas of steam and material gas until the temperature of a reforming catalyzer goes down to 400° C., cooling is performed in a range of 400-300° C. while purging the material gas by flowing steam, and cooling is performed at or under 300° C. while flowing air to purge steam.
Further, as shown in FIG. 10 of Patent Document 3, in a shutdown method for a reformer, cooling is performed by natural cooling by stopping steam and reforming gas until the temperature of the reforming catalyzer goes down to 400° C., cooling is performed in a range of 400-300° C. while purging the material gas by flowing steam, and cooling is performed at or under 300° C. while purging the steam by flowing air.
Further, as shown in FIG. 11 of Patent Document 3, in a shutdown method for a reformer, cooling is performed by flowing a mixture of steam and material gas until the temperature of the reforming catalyzer goes down to 400° C., and cooling is performed at or under 400° C. while purging the steam and the material gas by flowing nitrogen.
Further, as shown in FIG. 12 of Patent Document 3, in a shutdown method for a reformer, cooling is performed by natural cooling by stopping steam and material gas until the temperature of reforming catalyzer goes down to 400° C., and cooling is performed at or under 400° C. while purging the steam and the material gas by flowing nitrogen.    Patent Document 1. Japanese unexamined, published patent application No. 2002-8701    Patent Document 2. Japanese unexamined, published patent application No. 2002-151124    Patent Document 3. Japanese unexamined, published patent application No. 2002-93447